His impressive skills as an amateur cook on TV's MasterChef have amazed judges and swept him through to the semi-finals.

But Jonny Stevenson's progress should come as no surprise - as he has worked in a restaurant kitchen for nearly 18 months.

The rules of the BBC2 culinary show stress contestants must be amateurs and not professionals. Yet the dad of two, 32, helps prepare food at a diner two nights a week. And a Daily Mirror team watched him haul chunks of meat from a freezer to be used in dishes.

A show source blasted yesterday: "The judges were amazed at how quickly he caught on and how good he was, but of course he's good - he's worked in a kitchen.

"He's up against retired policeman, teachers and IT workers. It's not fair and he doesn't deserve to be there."

Viewers have heard Jonny, of Lisburn, Co Antrim, say: "I've learned loads in two days and I think I'll learn more."

Last night the BBC insisted he was not a chef and his part-time job merely involved reheating pre-packaged food.

Jonny, confronted by the Mirror outside the diner in his hometown, insisted show bosses knew - but he had no idea why they had not made it clear to viewers.

He said: "I get paid to put out kids' meals. The BBC are fully aware. I don't consider it as a chef." A BBC spokesman added: "He began working in a diner part-way through filming.

"His job involves re-heating pre-packaged foods. He does not do any cooking from scratch. This is entirely in keeping with the rules of MasterChef.

"Production staff and fellow contestants were aware of his part-time job and it does not put him in a beneficial position ahead of other contestants."